Originally posted by bowtime:
...On uphill the arrow is pulling against gravity.... so you must hold above the target overcoming the pull...
With all due respect, this is absolutely wrong. You cut yardage or hold lower for both up & down hill shots. The greater the angle up or down or the greater the distance, the more you have to cut.
Mark has it exactly right. It's the horizontal distance that is the "true" yardage.
However, you are right that this is due to gravity. A projectile is falling at 32 feet per second per second (remember freshman physics) In the real world, it doesn't matter if it is perfectly horizontal or at an angle. The only thing that affects this is if the projectile is getting lift from it's shape or some sort of wings.
If you have to hold higher on uphill shots, it's likely that you are not bending at the waist and simply raising your bow arm. This has the effect of reducing your draw length.
If you don't believe me, check with any of the compound field archers. They spend a huge amount of time getting their "cuts".
Of course I totally agree with Terry that it's best to figure this out for yourself through practice. Get in a tree, find a hill and shoot until it is subconscious.
Allen